The electromyogram of cat colon is affected by hypoxia and 2,4 Dinitrophenol. The perisistense of slow waves and migrating spike bursts during exposure to 0% O2 and 2,4 Dinitrophenol 10 to the minus 4th power M suggests that the genesis of slow waves and of migrating spike bursts in cat colon is not exclusively dependent on oxidative metabolic pathways. In the rabbit colon, the proximal colon has taenia coli, but the distal colon has none. The electromyogram can be recorded from the colon either with or without taenia coli. The electromyogram can also be recorded from both the serosal and mucosal sides of the rabbit colon. This is quite different from the cat colon, because the electromyogram can only be obtained from the mucosal side of the colon. The circular and longitudinal muscle strips of cat colon were exposed to some cholinergic drugs and tetrodotoxin. Both longitudinal and circular muscle were affected by cholinergic drugs (acetylcholine, physostigmine, and atropine). In addition, ciruclar muscle was affected by tetrodotoxin. This finding suggests that circular muscle is also under the control of a tonic inhibitory innervation.